Problem with ExportFactory

I'm trying MEF 2 Preview 1 but when I try to use ExportFactory (desktop app) I get this strange exception

FatalExecutionEngineError

The runtime has encountered a fatal error. The address of the error was at 0x670dac23, on thread 0x1bc0. The error code is 0xc0000005. This error may be a bug in the CLR or in the unsafe or non-verifiable portions of user code. Common sources of this bug
include user marshaling errors for COM-interop or PInvoke, which may corrupt the stack.